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Critical Studies/Book Reviews 1. Introduction 255 Critical Studies/Book Reviews David Hilbert. David Hilbert’s lectures on the foundations of geometry, 1891–1902. Michael Hallett and Ulrich Majer, eds. David Hilbert’s Foun- Downloaded from dational Lectures; 1. Berlin: Springer-Verlag, 2004. ISBN 3-540-64373-7. Pp. xxviii + 661.† Reviewed by Victor Pambuccian∗ http://philmat.oxfordjournals.org/ 1. Introduction This volume, the result of monumental editorial work, contains the German text of various lectures on the foundations of geometry, as well as the first edition of Hilbert’s Grundlagen der Geometrie, a work we shall refer to as the GdG. The material surrounding the lectures was selected from the Hilbert papers stored in two Gottingen¨ libraries, based on criteria of relevance to the genesis and the trajectory of Hilbert’s ideas regarding the foundations of geometry, the rationale, and the meaning of the foun- at Arizona State University Libraries on December 3, 2013 dational enterprise. By its very nature, this material contains additions, crossed-out words or paragraphs, comments in the margin, and all of it is painstakingly documented in notes and appendices. Each piece is pre- ceded by informative introductions in English that highlight the main fea- tures worthy of the reader’s attention, and place the lectures in historical context, sometimes providing references to subsequent developments. It is thus preferable (but by no means necessary, as the introductions alone, by singling out the main points of interest, amply reward the reader of English only) that the interested reader be proficient in both German and English (French would be helpful as well, as there are a few French quotations), as there are no translations. Chapter 1 consists of manuscript notes in Hilbert’s own hand for a course on projective geometry held in Konigsberg¨ in the summer semester of 1891; Chapter 2 is his own notes for a course on the foundations of geometry in Konigsberg,¨ planned for the summer of 1893, but held during the summer semester of the following year; Chapter 3 contains Hilbert’s notes for two Ferienkurse for high-school teachers which took place in Gottingen¨ in 1896 and 1898. Perhaps the most interesting of all, is Chapter 4. It consists of two versions of notes for a course on the † I thank John Baldwin, Michael Beeson, Robin Hartshorne, Marvin Greenberg, and Horst and Rolf Struve for their criticism, suggestions, and corrections of an earlier version. ∗ School of Mathematical and Natural Sciences, Arizona State University — West Cam- pus, Phoenix, Arizona 85069-7100, U.S.A. [email protected]. Philosophia Mathematica (III) Vol. 21 No. 2 C The Author [2013]. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: [email protected] 256 PHILOSOPHIA MATHEMATICA foundations of Euclidean geometry, delivered during the winter semester 1898/1899 in Gottingen.¨ These notes form the basis of the GdG of 1899, and contain a wealth of information of a strictly mathematical nature, which never made it into any edition of the GdG, and a wealth of state- ments relevant to both Hilbert’s motivations for proceeding the way he does and his philosophical views on the nature of the axiomatic enterprise. Downloaded from Unlike the Hilbert of GdG, with his extreme concision, the Hilbert we encounter in these lectures is talkative and opens a window to his mathe- matical mind’s house, allowing us glimpses of his aims and thoughts, and their gradual change with the passage of time. Chapter 5 contains the text of the first edition of the GdG, — a book that has become, like many first http://philmat.oxfordjournals.org/ editions, a rarity1 — referred to as the Festschrift, as it was written on the occasion of the unveiling of the Gauss-Weber monument. The introduction to Chapter 5 refers succinctly to the various editions that followed, with- out going into details regarding the changes. The reader who would like to have a synopsis of all these changes, all the way up to the eighth edition, should consult [Hilbert, 1971]. Chapter 6, the last one, contains a version of Hilbert’s lectures on the foundations of geometry delivered during the summer semester of 1902. This offers all interested researchers material that has been first interpreted in [Toepell, 1986], but had been available at Arizona State University Libraries on December 3, 2013 only through selected quotations. We will focus in this review on the following topics: (i) Hilbert’s view on the process of axiomatization and on the nature of geometry, as can be read from the material in the lectures; (ii) the specific questions raised in the lectures as providing a road map for the advances in the foundations of geometry obtained during the twentieth century and beyond; (iii) interest- ing material that can be found in the lectures, but not in GdG; and (iv) the legacy of the GdG. 2. The Process of Axiomatizaton and the Nature of Geometry Ad (i). First of all, one finds that Hilbert is very far in practice from formalism in the wide sense (as emphasized by Corry [2000; 2002; 2006] repeatedly) in which mathematics becomes a game with strict rules that manipulates meaningless formulas. His formalism is only a tool by which he tried to prove the consistency of arithmetic. In the practice of the axiomatization of geometry he did what his predecessors, Pasch, Peano, Pieri, had done as well, namely imagine an axiom system that does not require an understanding of either the entities or the predicates of the lan- guage in which it is expressed, that would go beyond having grasped their 1 It will likely become even more of a rarity, as university libraries in the United States have been discarding it, given that it was superseded by newer editions. One such discarded copy of the Festschrift was saved in the twenty-first century by Alexander Soifer for US$1. CRITICAL STUDIES/BOOK REVIEWS 257 characteristics as stipulated by the axioms of the axiom system. In fact, one is surprised to find that, although his empiricism is not as strict as that of Pasch — whose empiricism has recently been the subject of intense scrutiny [Gandon, 2005; Schlimm, 2010] — he shares with Pasch the view that geometry corresponds to aspects of our experience. On page 171 he notes, for example, that the Parallel Postulate and the Archimedean Axiom Downloaded from do not have the empirical2 character of the other axioms that allow con- struction by a finite number of experiments. On page 302 we read that ‘geometry is the the most accomplished natural science’,3 on page 303 that the task of the foundations of geometry is that of ‘a logical analysis of our intuition’s capabilities’,4 on page 391 that ‘the geometric theorems http://philmat.oxfordjournals.org/ are never true in nature in full exactness, since the axioms are never ful- filled by objects’, but that this should not be taken to be a flaw, for it is a characteristic of theories, for ‘a theory, that would coincide in all details with reality, would be no more than an exact description of the objects’. Another remarkable feature of Hilbert’s approach to the axiomatization of Euclidean geometry is the high regard which he has for Euclid, whom he is proud to correct or outwit sometimes. The entire enterprise, of turning geometry back into the deductive art it once was in ancient Greece, away from the ars calculandi that the analytic geometry ‘premisses’ of another at Arizona State University Libraries on December 3, 2013 age had turned geometry into,5 appears to have taken a page from Johann Joachim Winckelmann, whose credo was ‘Der einzige Weg f¨ur uns, groß, ja, wenn es moglich¨ ist, unnachahmlich zu werden, ist die Nachahmung der 2 Hilbert’s own emphasis. 3 ‘Geometrie ist die vollkommenste Naturwissenschaft.’ 4 ‘eine logische Analyse unseres Anschauungsvermogens’.¨ On the first page of the GdG itself, we find that the task of the book amounts to ‘the logical analysis of our spatial intuition.’ (‘die logische Analyse unserer raumlichen¨ Anschauung’ (p. 436)) 5 ‘Mit diesen Pramissen¨ ist dann sofort aus der Geometrie eine Rechenkunst geworden’ (p. 222). By creatively restoring elementary geometry to its former state, to an undertak- ing confined to its own language, without algebraic admixtures, Hilbert finds a solution to the critique expressed often by Newton of the Cartesian approach (for an in-depth look at Newton’s pronouncements regarding geometry and algebra see [Guicciardini, 2009]), such as in: ‘Anyone who examines the constructions of problems by the straight line and circle devised by the first geometers will readily perceive that geometry was contrived as a means of escaping the tediousness of calculation by the ready drawing of lines. Consequently these two sciences ought not to be confused. The Ancients so assiduously distinguished them one from the other that they never introduced arithmetical terms into geometry; while recent people, by confusing both, have lost the simplicity in which all elegance of geometry consists’ [Newton, 1673/83, p. 428]. Hilbert expresses a similar view in the 1898–99 lec- tures: ‘However, if science is not to fall prey to a sterile formalism,thenitmust reflect in a later stage of its development on itself, and should at least analyse the foundations that led to the introduction of number.’ (‘Aber, wenn die Wissenschaft nicht einem unfruchtbaren Formalismus anheimfallen soll, so wird sie auf einem spateren¨ Stadium der Entwicklung sich wieder auf sich selbst besinnen mussen¨ und mindestens die Grundlagen pr¨ufen,auf denen sie zur Einf¨uhrungder Zahl gekommen
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